A sensor network, which is called a wireless sensor network or a ubiquitous sensor network, is a network including a plurality of sensor nodes and a sink node which sends information of the sensor node to the outside. For the automated remote information collection, the sensor node senses, processes, and collects various information.
To continuously sense and transmit necessary data at a specific location, the sensor node in the sensor network needs to operate for a long time with a low power. Accordingly, it is necessary to operate the sensor node with the limited battery capacity for a time intended by a user. For doing so, it is required to predict the accurate battery use time and to set a sensing cycle according to the prediction. In general, the battery use time of the sensor node is predicted using a method which divides the remaining battery capacity by the energy consumed by the sensor node.
Since this method sets the sensing cycle by dividing the remaining battery capacity by the energy consumed by the sensor node, there is an error between the calculated battery use time and the actual battery use time and the error range expands with time.
FIG. 1 is a graph of a lifetime prediction error rate based on the time in a conventional sensor node. FIG. 1 shows the error rate of the difference between the actual operation time per hour and the predicted operation time based on the remaining battery capacity when the sensor node operates for 20 hours. The sensor node performs high-workload and low-workload in two environments with 50% duty cycle. Herein, the high-workload continuously senses and then immediately transmits data over the radio, and the low-workload senses once per 1 minute and then sends data over the radio. The 50% duty cycle iterates the sensing and the data transmission per 30 seconds.
As shown in FIG. 1, there is the great difference between the battery use time calculated using the general method and the actual battery use time, and the error range expands as the time goes by. This is because the sensing cycle is randomly set based on the inaccurate information. In result, the use time of the USN node is inaccurately predicted.